In general, a cutting insert has a shape corresponding to a rectangular solid having six surfaces, including an upper surface, a lower surface, and four side surfaces, wherein the upper surface and the lower surface have an assembling hole formed through them and each of the upper surface and the lower surface has a major cutting edge and a minor cutting edge formed in the diagonal direction thereof.
The major cutting edge and the minor cutting edge are rotationally symmetrical to each other with respect to the center of the rectangular solid, i.e. the cutting insert, so as to allow the cutting insert to be also used in an inverted state or a rotated state.
Korean Patent No. 10-0718306 entitled “Cutting Insert” and filed by and issued to the applicant of the present invention discloses a conventional cutting insert.
The upper surface and the lower surface of the conventional cutting insert are symmetrical to each other to be rotated by 180 degrees with respect to an imaginary center by which a major side surface is divided into upper and lower sides. The upper surface and the lower surface includes first corner cutting edges higher than the upper surface and the lower surface and second corner cutting edges lower than the upper surface and the lower surface respectively at two corners thereof.
Inclined major cutting edges are formed between the first corner cutting edges and the second corner cutting edges respectively, and minor cutting edges are formed between the first corner cutting edges and the second corner cutting edges facing each other along minor side surfaces.
Meanwhile, each of the minor cutting edges includes a first inclined cutting edge, a second inclined cutting edge, a grooved minor cutting edge, and a flat cutting edge.
The cutting insert is mounted to a cutting tool, and a cutting performance of the cutting insert may be significantly varied depending on an inclination angle of a major cutting edge with respect to a direction where the cutting insert progresses when a work piece is cut.
An angle between a machined surface of a work piece and a major side surface is called a marginal angle, and frictional heat is generated between a cutting insert and the work piece depending on a magnitude of the marginal angle, greatly influencing a life span of the cutting insert.
A double-sided cutting insert employs major cutting edges on an upper and a lower surface thereof, in which case a posture of the cutting insert is determined when the cutting insert is mounted to a cutting tool so as to secure a marginal angle.
If the marginal angle is set and fixed according to the posture of the cutting insert, the above-described inclination angle is determined depending on an angle between the major cutting edge and a side surface of the cutting insert, in which case cutting performance is significantly varied depending on the inclination angle.
However, the conventional cutting insert secures only marginal angles of major cutting edges, but fails to secure any marginal angle on sides of minor cutting edges. In more detail, a side surface of the conventional cutting insert is perpendicular to a horizontal reference surface in a drawing where the side surface is the front.
Accordingly, although a marginal angle for reducing friction between the conventional cutting insert and a work piece may be secured in an angle between a side surface of the cutting insert and a surface of the work piece when the cutting insert is mounted to a tool, since a negative marginal surface is formed in terms of an angle between the major cutting edge and the work piece, it is necessary for the double-sided cutting insert to have a marginal angle for decreasing frictional heat and a marginal angle for improving cutting performance.